Low-energy structure of six-dimensional open-string vacua

TL;DR

This dissertation explores the low-energy effective actions of six-dimensional open-string models, focusing on anomaly cancellation, supersymmetry breaking, and the detailed structure of brane-world scenarios.

Contribution

It provides a comprehensive analysis of anomaly cancellation mechanisms and supersymmetry breaking in six-dimensional open-string models, including original results on coupling supergravity to matter and brane-induced supersymmetry breaking.

Findings

Complete coupling of (1,0) supergravity to matter multiplets

Anomaly cancellation via Green-Schwarz mechanism without fixing gaugino couplings

Non-linear realization of supersymmetry on branes in specific models

Abstract

This dissertation reviews some properties of the low-energy effective actions for six dimensional open-string models. The first chapter is a pedagogical introduction about supergravity theories. In the second chapter closed strings are analyzed, with particular emphasis on type IIB, whose orientifold projection, in order to build type-I models, is the subject of the third chapter. Original results are reported in chapters 4 and 5. In chapter 4 we describe the complete coupling of (1,0) six-dimensional supergravity to tensor, vector and hypermultiplets. The generalized Green-Schwarz mechanism implies that the resulting theory embodies factorized gauge and supersymmetry anomalies, to be disposed of by fermion loops. Consequently, the low-energy theory is determined by the Wess-Zumino consistency conditions, rather than by the requirement of supersymmetry, and this procedure does not fix a quartic coupling for the gauginos. In chapter 5 we describe the low-energy effective actions for type-I models with brane supersymmetry breaking, resulting form the simultaneous presence of supersymmetric bulks, with one or more gravitinos, and non-supersymmetric combinations of BPS branes.The consistency of the resulting gravitino couplings implies that local supersymmetry is non-linearly realized on some branes. We analyze in detail the ten-dimensional $USp(32)$ model and the six-dimensional (1,0) models.